It is recommended that diabetic patients perform a daily self-management of diabetes by measuring blood sugar level variations by themselves. For the purpose of the measuring, there has been put to practical use a blood component measuring device. The blood component measuring device measures blood glucose levels by mounting a test paper impregnated with a reagent, which gives a color depending on the amount of glucose in blood, applying blood to the test paper to cause the test paper to produce a color, and optically measuring the degree of the color for thereby determining and displaying the blood glucose level.
In order for a patient to sample his or her own blood, the patient uses a puncture instrument equipped with an axially movable needle. As disclosed in Japanese Laid-Open Patent Publication No. 2007-536008 (PCT) (WO2005/110227A1), for example, such a puncture instrument employs a drive spring for axially biasing the needle. When the drive spring expands from a compressed state, it causes the needle to project instantaneously and puncture the skin, e.g., a finger, a palm, an arm, or the like, of the patient, for thereby allowing a small amount of blood to flow out. After the skin is punctured, the needle is pulled from the skin and retracted into a housing by a return spring, which is separate from the drive spring.